Removal of straight chain hydrocarbons from different hydrocarbon stocks

ABSTRACT

A cyclic process is disclosed for sequentially treating two different naphtha stocks in the same molecular sieve adsorption bed to produce nonstraight chain hydrocarbon fractions respectively from each stock and a third product composed of straight chain hydrocarbons from both stocks. Also disclosed is the use of this procedure in conjunction with a reforming process wherein a naphtha feed is first denormalized, the denormalized naphtha is reformed and the resulting reformate is denormalized to yield high octane gasoline blending stock.

United States Patent [191 Glessner et al.

REMOVAL OF STRAIGHT CHAIN HYDROCARBONS FROM DIFFERENT HYDROCARBON STOCKSInventors: Alfred J. Glessner, Glenolden, Pa.; William WayneWentzheimer, Edgewood, Md.

Sun Oil Company of Pennsylvania, Philadelphia, Pa.

Filed: Aug. 24, 1971 Appl. No.: 174,322

Assigneez U.S. Cl..... ..208/85, 208/310, 260/676 MS Int. Cl. ..C10g25/04, C10g l/00, Cl0g 35/18 Field of Search ..208/310, 85; 260/676 MSReferences Cited UNITED STATES PATENTS Fleck et al ..208/310 Kimberlinet al. ..260/676 MS 1 Mar. 27, 1973 2,987,471 6/1961 Eggertsen ..208/3103,007,863 11/1961 Hess et al. ..208/31O 3,268,440 8/1966 Griesmer et a1...208/310 3,520,801 7/1970 Lewis et al. .208/3 10 PrimaryExaminer-Herbert Levine Attorney-George L. Church et a1.

[57] ABSTRACT 8 Claims, 2 Drawing Figures l6 j PURGE GAS 8 n-PARAFFINSPURGE GAS7 18 G/5L "A" RAFFINATE Q/ "B" RAFFINATE PAIEI-IIEDIIARZYIQYBPURGE GAS SHEET 1 [IF 2 FIG. I

"A" RAFFINATE ;\D "B" RAFFINATE INVENTORS ALFRED J. GLESSNER WILLIAMWAYNE WENTZHEIMER BY 7 -MWM y ATTORNEY PATEr-fliinmzmrs 3,7 3,292

SHEET 2 BF 2 FIG. 2

- 44 I 3o NAPHTHA 5 E FEED 32 SEPARATOR ADSORBER f lz n-PARAFFINS 2 sGASOLINE s z BLENDING [H2 RECYCLE 55 34 M STOCK 1 56 0 REFORMERSEPARATOR INVENTORS W. 2 -MW, F.

ATTORNEY REMOVAL OF STRAIGHT CHAIN HYDROCARBONS FROM DIFFERENTHYDROCARBON STOCKS CROSS REFERENCE TO RELATED APPLICATION Copendingapplication Ser. No. 112,140, filed Feb. 3, 1971, by Alfred J. Glessner,William Wayne Wentzheimer and Rene F. Kress, describes a processinvolving denormalizing naphtha by means of molecular sieves,hydroforming the denormalized naphtha and then denormalizing thereformate by means of molecular sieves. The present invention isapplicable for carrying out the two denormalization steps of thatprocess in an improved manner.

BACKGROUND OF THE INVENTION This invention relates to an adsorptionprocess for separating each of two different naphtha feedstocks intostraight chain and nonstraight chain hydrocarbon fractions by treatmentwith a molecular sieve adsorbent.

It is well known that hydrocarbon stocks such as gasoline and kerosenecan be treated in either vapor or liquid phase with crystalline zeolitemolecular sieves having uniform pore diameters of about 5 Angstrom unitsto selectively adsorb n-paraffins and unbranched olefins from the otherhydrocarbon components. This type of treatment has been described innumerous United States Patents of which the following are examp les:Pat. No. 2,886,508, H. V. Hess et al., issued May 12, 1959; No.2,917,449, E. R. Christensen et al., issued Dec. 15, 1959; No.2,945,804, C. E. Hemminger, issued July 19, 1960; No. 2,952,614, K. E.Draeger et al., issued Sept. 13, 1960; Nos. 2,958,644 and 2,958,645, C.N. Kimberlin, Jr., et al., both issued Nov. 1, 1960; and No. 3,193,490,D. B. Boughton, issued July 6, 1965.

There are instances where in processing two different stocks in refineryoperations it is desirable to separate each stock into straight chainand nonstraight chain hydrocarbon fractions. Several processes in whichtwo different stocks are treated with zeolitic molecular sieves for thispurpose have been described in the following United States Patents: No.2,891,902, H. V. Hess et al., issued June 23, 1959; No. 2,935,467, R. N.Fleck et al., issued May 3, 1960; No. 2,944,001, C. N. Kimberlin, Jr.,et al., issued July 5, 1960; No. 2,987,471, F. T. Eggertsen, issued June6, 1961; No. 3,007,863, H. V. Hess et al., issued Nov. 7, 1961; No.3,160,581, W. J. Mattox et al., issued Dec. 8, 1964; and No. 3,227,647,H. G. Krane, issued Jan. 4, 1966.

The present invention is applicable to such refinery operations whereintwo different stocks boiling in the range of gasoline and kerosene areto be processed to selectively separate straight chain from nonstraightchain hydrocarbons. These stocks can have boiling ranges which areeither substantially the same or different. The invention can be used asan improved way of practicing the adsorption operations in the severalprocesses of the above-mentioned patents in which different stocks aretreated with molecular sieve adsorbents.

SUMMARY OF THE INVENTION The invention involves a cyclic operation forthe successive treatment of two naphtha stocks in an adsorption zonecontaining zeolitic molecular sieves and the separate recoveryofraffinate products (i.e. nonstraight chain hydrocarbons). The extractmaterials (i.e. straight chain hydrocarbons) from the two stocks arerecovered entirely or in part in admixture with each other.

The cyclic method of utilizing the adsorbent according to the inventioncomprises the following steps with steps A to G, inclusive, being insequence:

A. introducing a first'feed in vapor form into one end of a bed ofmolecular sieve adsorbent selective for adsorbing straight chainhydrocarbon and passing same toward the other end;

B. stopping introduction of the first feed before the amount introducedis sufficient to saturate the adsorbent with straight chain hydrocarbon;

C. introducing a purge gas into the bed in amount to purge interstitialhydrocarbons therefrom without substantial displacement of adsorbedstraight chain hydrocarbon;

D. introducing a second feed in vapor form into said one end of the bedand passing same toward the other end;

E. stopping introduction of the second feed at least before straightchain hydrocarbon of highest molecular weight from the feed having thelower end boiling point appears in the effluent or, in some embodimentsof the invention, before any substantial amount of any straight chainhydrocarbon appears in the effluent;

F. introducing purge gas into the bed in amount to purge interstitialhydrocarbons therefrom without substantial displacement of adsorbedstraight chain hydrocarbon;

G. introducing a further quantity of purge gas into said other end ofthe bed until substantially all straight chain hydrocarbons have beendisplaced therefrom through said one end;

H. segregating the effluent from said other end of the bed into separateproduct fractions comprising a first product rich in nonstraight chainhydrocarbons from the first feed and a second product rich innonstraight chain hydrocarbons from the second feed;

I. and recovering from the effluent from said one end of the bed a thirdproduct comprising straight chain hydrocarbons from both feeds.

In another aspect the invention is applicable to a process for upgradinga feed naphtha of the C C range involving treatment of the naphtha in anadsorption zone containing molecular sieves to separate same inton-paraffin-rich and n-paraffin-lean fractions in a manner preferablysuch that the latter still contains nparaffins of the C,,-C range,catalytically reforming the n-paraffin-lean fraction, and treating theresulting reformate in the same adsorption zone to yield denormalizedreformate. In this procedure C -C n-paraffins from the feed naphthatogether with any C-,-C nparaffins formed during the reforming step areobtained from the adsorption zone as a single product, while n-paraffinsof the C,,C range from the feed naphtha as well as from the reformateare included in the n-paraffinlean fraction which is reformed. These C-C6 n-paraffins are converted during the reforming operation mainly to CC isoparaffins which end up as components of the denormalized reformate.

BRIEF DESCRIPTION OF DRAWINGS The invention is described in conjunctionwith the accompanying drawings wherein:

FIG. 1 schematically illustrates a single adsorption zone operated in acyclic manner to denormalize two different feeds designated as A and B.

FIG. 2 is a schematic flowsheet of a reforming process wherein theinvention is utilized for denormalizing the fresh feed naphtha as wellas the reformate produced.

DESCRIPTION The present invention has utility in refinery operationswherein two different feed materials of either similar or differentboiling ranges are to be denormalized. The term denormalize as usedherein refers to removing straight chain hydrocarbons, which can benparaffins or nonbranched aliphatic olefins or both, from nonstraightchain hydrocarbons.

The invention is especially useful when it is desired to denormalize oneof the stocks substantially completely while exhaustive removal ofstraight chain hydrocarbons from the other stock is not essential. Anexample of such a situation in refinery practice is when one of thestocks is to be employed in a low octane gasoline pool while the otheris to be used for making gasoline of high antiknock quality, forexample, lOO or more F-l clear octane number. In such case the presenceof a small amount of n-paraffins in the firstmentioned blending stockcan readily be tolerated whereas even a small percentage of n-paraffinsin the other may be highly detrimental.

The invention also has special applicability in conjunction with thereforming process described in aforesaid application Ser. No. 112,140.

FIG. 1 illustrates an adsorption zone 10 containing a bed of crystallinezeolite molecular sieves having uniform pore diameter of about 5Angstrom units. The adsorption zone is utilized in a cyclic operation inwhich feed naphthas A and B are sequentially treated in vapor phase andadsorbed straight chain hydrocarbons from both feeds are then desorbedby means of a purge gas. More specifically, feed A at elevatedtemperature is first introduced through line 11 and valve 12 into thetop of the bed and passed downwardly toward the bottom. The temperaturein the adsorbent can be in the range of 300-800F. (l49427 C.), morepreferably 350750F. (177-399C.), and is sufficiently high to maintainthe feed as a vapor at the prevailing pressure but not so high as tocause cracking. In each cycle the amount of feed A introduced issubstantially less than that amount which would saturate the adsorbentwith straight chain hydrocarbons. For example the amount introduced percycle generally will be between 5 percent and 80 percent of the amountwhich would fully saturate the adsorbent with straight chainhydrocarbons. For purpose of description the latter here are consideredto be n-paraffins. As the feed A material passes downwardly in the bedthe n-paraffins are retained in the upper portion of the adsorbent whilebranched and cyclic hydrocarbons pass on down the bed and out of thebottom, from which they are collected through valve 17 and line 18 as Araffinate. This product is of especially high purity since it has passedthrough a considerable amount of adsorbent that has not been saturatedwith n-paraffins.

After the desired amount of feed A has been introduced, its flow to thebed is stopped and a heated purge gas is introduced in amount sufficientonly to force interstital hydrocarbons from the bed without substantialdisplacement of the adsorbed n-paraffins. Any suitable gas can be usedas the purge gas, such as hydrogen, methane, ethane, propane, nitrogen,carbon dioxide, carbon monoxide and the like. The purge gas can beintroduced at the top or bottom of the bed so as to force theinterstitial hydrocarbons toward either end, but it is distinctlypreferable that it be introduced at the bottom in order to displace theinterstitial hydrocarbons in the opposite direction from which theyentered. This permits the displaced hydrocarbons to be sent back throughvalve 12 into feed line 11 and eliminates any need for separatelycollecting this material in order to avoid product contamination. Thusthe displaced hydrocarbons will again enter adsorption zone 10 in asubsequent cycle of operation along with additional feed A.

Feed B is next introduced in vapor phase and likewise at elevatedtemperature into the top of adsorption zone 10 through line 13 and valve14 and passed downwardly in the bed. The bed temperature again ismaintained in the ranges previously specified. Preferable the additionof feed B is continued until the adsorbent has become saturated withn-paraffins substantially throughout its entire mass, as this permitsmost efficient utilization of the adsorbent in each cycle. In any eventintroduction of feed B is stopped at least before the n-paraffin ofhighest molecular weight of the feed having the lower end boiling pointappears in the effluent from the bottom of the bed. For example, if feedA contains n-paraffms through the range of C -C while feed B containsthose of the higher boiling range that includes C C then theintroduction of feed B would be stopped at least before n-octane appearsin the effluent. In some embodiments of the invention, introduction offeed B is stopped before effluent from the bottom of the bed exhibitssubstantial content of any nparaffins. During this stage the effluentpassing from the bottom of zone 10 is separately collected through valve19 and line 20 as B raffinate. This product may not have as high purityas A raffinate but in any event itsn-paraffin content will be low.

The next step in the cycle involves again introducing heated purge gasto adsorber 10 to remove interstitial hydrocarbons from the bed withoutsubstantial displacement of the n-paraffins. Preferably this is alsodone by passing purge gas from line 21 and valve 22 into the bottom ofthe adsorber to push the interstitial hydrocarbons upwardly through thebed. Again the amount of purge gas used is just sufficient to purge outthe interstitial hydrocarbons without substantial displacement of then-paraff'ms from the bed. The removed hydrocarbons preferably areallowed to flow back through valve 14 into line 13, from which they willthereafter be fed along with additional feed B to adsorber 10 in asubsequent operating cycle.

After purging of the interstitial hydrocarbons from the bed, a furtherquantity of hot purge gas is then passed through line 21 and valve 22upwardly through the bed in amount to desorb and displace from theadsorbent substantially all n-paraffins which were adsorbed from feeds Aand B during the present cycle. The effluent from the top of the bed,containing the displaced n-paraffins and purge gas, is separatelycollected through valve and line 16. The n-paraffins, which can berecovered by condensation from this stream upon cooling are a mixture ofthe n-paraffin components of both feed A and feed B.

The above-described procedure, wherein the adsorbent bed is desorbed ina direction opposite from instead of the same as that in which the feedmaterials were introduced, is particularly advantageous when the feedscontain a plurality of n-paraffins. As the number of carbon atoms permolecule increases the adsorbability thereof by molecular sieveslikewise increases. Consequently n-paraffins of different molecularweights will progress through the adsorbent bed at different rates andtend to segregate into adjacent zones. After the feed materials havebeen introduced, the heaviest n-paraffin will be nearest the inlet endwhile the lightest will concentrate toward the opposite end. Desorbingthese components in a direction opposite to that at which they enteredfacilitates their removal from the bed, since the most strongly adsorbedcomponent has to travel the least distance to leave the bed. Thisresults in a saving in amount of desorbing gas and time needed fordesorption.

Another improvement in the desorption efficiency can be effected bydesorbing only part of the n-paraffins from the bed when the cyclicoperation is first started and thereafter desorbing only to this same extent during each cycle. This leaves a residual amount of n-paraffins inthe bed in each cycle, which residue will be mainly the n-paraffin ofhighest molecular weight that was present in feeds A and B. The amountof purge gas then used in each cycle is that necessary for keeping theamounts of n-paraffins charged to and removed from the bed in the samecycle in balance. In other words the amount of purge gas introducedduring a cycle is such that the quantity of n-paraffins desorbed isabout the same as the total quantity adsorbed from the portions of feedsA and B just introduced and not such amount as to displace alln-paraffins from the bed. By leaving this n-paraffin residue, less purgegas is required than otherwise would be needed.

While FIG'. 1 shows only one adsorber 10, in practice a plurality ofadsorber beds normally would be used in parallel so that the naphthafeeds could be fed from a common manifold alternately to the beds intimed sequence to permit continuous introduction of each naphtha to thesystem. Each bed would operate on a time cycle involving stages ofadsorption of the straight chain hydrocarbons from the two feedmaterials, purging stages for removing interstitial hydrocarbons and thedesorption stage for displacing the n-paraffins from the adsorbent, allas above described. In each cycle predetermined amounts of each feedwould be introduced to each bed such that the total quantity of straightchain hydrocarbons so introduced preferably would be enough toapproximately saturate the molecular sieve adsorbent. The relativeamounts of the feed naphthas introduced per cycle can be calculated fromtheir straight chain hydrocarbon contents and the quantities of eachfeed to be processed per unit time. For example, if feed A and feed Bwill supply, respectively, 30 percent and percent of the total quantityof n-paraffins to be removed per day, then the amount of feed Aintroduced to a bed per cycle preferably is that which would saturate 30percent of the adsorbent, while the amount of feed B is that which willapproximately saturate the remaining 70 percent of the adsorbent.

FIG. 2 illustrates a process wherein a feed naphtha composed ofn-paraffins and non-n-paraffins of the C -C range is first treated withmolecular sieves, raffinate so obtained is then hydroformed whereby aminor but significant amount of n-paraffins is produced, and theresulting reformate is then treated with the same molecular sieves toobtain fully denormalized product of high antiknock value. A feature ofone embodiment of the process of FIG. 2 is that the adsorption operationis conducted in such a manner that n-paraffins of the C .,C range remainwith the raffinate which is fed to the reformer, while n-paraffins ofthe C C range are segregated as a separate product. This isadvantageous, as the C C n-paraffins will isomerize during the reformingstep to isomers useful as gasoline components whereas the highern-paraffins tend to react adversely, eg by cracking, and are undesirableas components of the reformer feed.

The feed to the process of FIG. 2 can be any naphtha fraction containingn-paraffins and other hydrocarbons of the C .,C, range including one ormore n-paraffins of the C C range. The feed can be a wide boiling ornarrow boiling fraction and may, for example, have an initial boilingpoint in the range of 50300F. (l0'l49 C.) and an endpoint in the rangeof 210475F. (99-246C.). The n-paraffin content of the feed can varywidely, e.g. 3-50 percent by weight. The feed can, for example, includeall of the n-paraffins of the C C range, or it can be narrower boilingso as to include only portions of the range such as C .,C n-paraffins orC --C n-paraffins or C C n-paraffins. The feed enters the system throughline 30 and is passed to heater 31 wherein it is vaporized and heated toa temperature in the range of 300800F. (l49427C.), more preferably350750F. l77-399C.). The vapors then pass to a manifold or surge zone(not shown) from which a plurality of adsorber beds can be alternatelyfed in timed sequence so that a continuous flow of vapors from themanifold to an adsorber will occur. For simplicity the adsorptionoperation is illustrated by the singly adsorber 33 to which the feednaphtha is introduced via line 32.

For the purpose of describing a cycle of operation of adsorber 33, it isconsidered that the cycle begins with the introduction thereto ofreformate rather than naphtha. At this time the molecular sieveadsorbent has just been desorbed and is substantially free ofhydrocarbons. The reformate, obtained as hereinafter described, ispassed through line 35 and heater 36 wherein it is vaporized and heatedto a similar temperature level as already stated above for the naphthafeed. The hot vapors then flow into another mainfold (not shown) fromwhich they are fed to adsorber 33 through line 37. The reformatetypically contains C,,C n-

paraffins as well as higher n-paraffins formed during the reformingreactions, and these n-paraffins are selectively adsorbed by themolecular sieves as the reformate flows down through the bed. Thenonadsorbed raffinate fraction, constituting the n-paraffinleanreformate material, is separately collected as a product through line39. This material has high antiknock value and is an excellent blendingstock for high quality gasoline.

Within the adsorbent bed a gradation in composition of the adsorbateoccurs due to the fact that, as previously explained, a higher molecularweight n-paraffin is more strongly adsorbed than a lower molecularweight n-paraffin. Consequently, in passing through the bed, the C -Cn-paraffins will forge ahead of the higher nparaffins. The amount ofreformate introduced per cycle is insufficient to saturate the molecularsieve adsorbent with C C, n-paraffins and consequently the C ,-Cn-paraffins do not reach the outlet until a later phase of the cycle.During the present phase the gaseous effluent which leaves the bottom ofadsorber 33 through line 39 is composed essentially of branched andcyclic hydrocarbons. This is the denormalized reformate product of theprocess.

After the introduction of reformate has been stopped, purge gas, whichis a portion of the hydrogen recycle stream from the reforming step, ispassed into the bottom of adsorber 33 by means of line 34. The amount ofpurge gas introduced is just sufficient to push the interstitialhydrocarbons out the top of the bed and back through line 37 to themanifold. Essentially no removal of n-paraffins from the adsorbentoccurs during this purging step.

In the next phase of the cycle, hot naphtha feed from line 32 isintroduced into the top of the bed and flows downwardly. Nonstraightchain hydrocarbons pass out of the bed through line 38 to theappropriate manifold, while the C -C n-paraffins are adsorbed and becomedistributed in accordance with molecular weight variations along thelength of the bed together with corresponding n-paraffins from thereformate. In one embodiment, addition of naphtha feed is stopped beforethe lightest n-paraffin appears in the effluent and subsequently alln-paraffins of the C C are desorbed and collected together as a separatefraction. However, in the preferred embodiment of the process of FIG. 2,feed naphtha is introduced through line 32 in amount sufficient todisplace at least most of the C C n-paraffins from the bed through line38 but insufficient to displace C,-C n-paraffins. The C,,C n-paraffinsmixed with nonstraight chain hydrocarbons of the feed naphtha pass fromline 38 to a manifold or surge zone (not shown), thus all becomingconstituents of the nparaffin-lean material collected therein for use asreformer feed.

After addition of feed naphtha to adsorber 33 has been stopped, purgegas is again introduced through line 34 in amountjust sufficient to pushthe interstitial hydrocarbons out of the bed. The displaced hydrocarbonsflow from the top back through line 32 to the corresponding manifold.

Finally, to complete the cycle, a large quantity of purge gas is fedthrough line 34 and passes upwardly through the bed in order to desorball of the n-paraffins. A mixture of purge gas and n-paraffins leavesthe top of the adsorber via line 40 and goes through cooler 41 whereinthe n-paraffms are condensed and then into gas-liquid separator 42.Recovered purge gas is removed from the top of the separator and sentthrough line 44 back to the hydrogen recycle gas system. From the bottomof separator 42 a C -C n-paraffin product is withdrawn through line 43.If desired, this product can be passed to a catalytic dehydrocyclizingoperation (not shown) for upgrading to high quality aromatic blendingstock.

The n-paraffin-lean naphtha fraction from the adsorber, which alsocontains the C -C n-paraffins as shown above, is passed through line 50to heater 51 wherein it is heated to a suitable reforming temperature,after which it is subjected to hydroforming as indicated by reformer 52.Any suitable reforming catalyst and conditions can be employed in thisstep. Typically the reforming reaction is carried out by means of aplatinum-containing reforming catalyst in the presence of hydrogen atsuitable reforming temperatures in the range of 750-l000F. and pressuresof from or 200 p.s.i.g. to 700 p.s.i.g. A space velocity generally inthe range of 05-20 liquid volumes per hour per volume of catalyst(v/hr./v) and usually of 2 or more, e.g. 3 v/hr./v, is utilized. Averagetemperatures in the reformer 52 may be, for example, in the range of875-975F. A plurality of reactors in series generally is used in thistype of operation, with heaters between reactors for reheating thehydrocarbon reactants to compensate for reductions in temperature thatoccur due to the endothermic reactions which take place. Under thesereforming conditions naphthenes dehydrogenate to aromatics, substantialisomerization of the C -C n-paraffins occurs, a significant portion ofthe C C or higher singly branched paraffins disappear by being convertedto other components, and also C and higher n-paraffins are formed insubstantial amount.

The effluent from reformer 52 is withdrawn through cooler 53 and passesto gas-liquid separator 54. The hydrogen-containing gas phase is in partrecycled from the top of separator 54 through lines 55 and 50 and heater51 back to reformer 52 and in part is withdrawn through line 34 for useas purge gas. A hydrogen recycle rate typically in the range of3,0009,000 SCF/bbl. of reformer feed is used and the hydrogen content ofthe recycle stream is generally in the range of 60-98 percent by volume.Any excess hydrogen can be removed from the system as indicated by line56.

Platinum-containing reforming catalysts are preferred for effecting thehydroforming reaction in reformer 52. Such catalysts have been describedin numerous prior art references and need not be described herein.Reference can be made, for example, to the following: CATALYTICPROCESSES AND PROVEN CATALYSTS by C. L. Thomas, pages 54-57, AcademicPress (1970); US Pat. No. 2,479,109, V. Haensel, issued Aug. I6, 1949;and US. Pat. No. 2,478,9I6, V. Haensel et al., issued Aug. 16, I949. Theplatinum-containing catalyst can also contain other metals, such asrhenium, ruthenium, rhodium or iridium, which are beneficial. ThepIatinum-rhenium reforming catalysts are particularly desirable and suchcatalysts have been described in US. Pat. No. 3,415,737, H. E.Kluksdahl, issued Dec. 10. I968 and U.S. Pat. No. 3,434,960, R. L.Jacobsenson, issued Mar. 25, 1969. Platinum-iridium reforming catalystsare disclosed in US. Pat. No. 3,554,902, W. C. Buss, issuedJan. 12,1971.

The liquid reformate which passes from the bottom of separator 54through line 35 contains C:,C n-paraffins which have not isomerized orwhich were produced by the reforming reactions and a significant amountof C and higher n-paraffins but is substantially depleted of singlybranched paraffms of the C C range or higher as compared to the chargeto reformer 52. This reformate is then treated in adsorber 33 in themanner previously described to selectively remove the n-paraffincomponents and yield blending stock of high antiknock value. v

The following is a specific example of processing in the manner of FIG.2 but without segregating C,,C from the higher paraffins. in this casethe process handles 10,000 bbls./day of a fresh naphtha cut containing-25 percent by volume of n-paraffins all of which are of the C C range.This amount per day of naphtha feed enters the adsorption zone 33 and7,500 bbls./day of denormalized naphtha substantially free of anyn-paraffins are produced through line 38. The denormalized naphtha isprocessed in reformer 52 utilizing a platinum-containing reformingcatalyst at an average temperature of 910F. and pressure of 350 p.s.i.g.The reformate product obtained from separator 54 through line 35 amountsto 6,375 bbls./day, has an R1 clear octane rating of about 100 andcontains a total of 6 percent-n-paraffins made up of 3.2 percent C,-,--Cn-paraffins and 2.8% C and higher n-paraffins. This shows thatn-paraffins are produced during the reforming operation. This reformateis fed to adsorber 33 through line 37 at the beginning of each cycle inthe manner previously described. After the phase of introducingreformate to the adsorption zone, each cycle includes the sequentialphases of purging interstitial hydrocarbons, feed fresh naphtha inamount insufficient to cause any n-paraffins to appear in the effluent,purging again and finally desorption of the n-paraffins from the bed inthe opposite direction from which they were introduced. This procedureresults in a denormalized reformate, obtained through line 39 in amountof 5,990 bbls./day having an F-l clear octane number of about 103. Alsoobtained is a product composed of n-paraffins of the C,,C range, whichis removed from separator 42 through line 43 in amount of 2,885bbls./day.

The invention claimed is:

1. In a process wherein two different naphtha feeds are separated intostraight chain and nonstraight chain hydrocarbon fractions by treatmentwith a molecular sieve adsorbent selective for adsorbing straight chainhydrocarbons, the method of utilizing the adsorbent in a cyclic mannercomprising the following steps with steps A to G, inclusive, being insequence:

A. introducing a first feed in vapor form into one end of a bed of saidmolecular sieve adsorbent and passing same toward the other end;

B. stopping introduction of the first feed before the amount introducedis sufficient to saturate the adsorbent with straight chain hydrocarbon;

C. introducing a purge gas into the bed in amount to purge interstitialhydrocarbons therefrom without substantial displacement of adsorbedstraight chain hydrocarbon;

D. introducing a second feed in vapor form into said one-end of the bedand passing same toward the other end;

E. stopping introduction of the second feed at least before straightchain hydrocarbon of highest molecular weight from the feed having thelower end boiling point appears in the effluent from said other end ofthe bed;

F. introducing purge gas into the bed in amount to purge interstitialhydrocarbons therefrom without substantial displacement of adsorbedstraight chain hydrocarbon;

G. introducing a further quantity of purge gas into said other endof thebed until substantially all straight chain hydrocarbons have beendisplaced therefrom through said one end;

H. segregating the effluent from said other end of the bed into separateproduct fractions comprising a first product rich in nonstraight chainhydrocarbons from the first feed and a second product rich innonstraight chain hydrocarbons from the second feed;

. and recovering from the effluent from said one end of the bed a thirdproduct comprising straight chain hydrocarbons from both feeds.

2. A process according to claim 1 wherein in each of steps C and F thepurge gas is introduced into the said other end of the bed to purgeinterstitial hydrocarbons from said one end.

3. A process according to claim 2 wherein in step E the introduction ofsaid second feed is stopped before any substantial amount of anystraight chain hydrocarbon appears in said effluent.

4. A process according to claim 1 wherein in step E the introduction ofsaid second feed is stopped before any substantial amount of anystraight chain hydrocarbon appears in said effluent.

5. In a process for upgrading a feed naphtha composed of n-paraffin andnon-n-paraffin hydrocarbons of the C,,C range by separating the feednaphtha into nparaffin-rich and n-paraffin-lean fractions andcatalytically reforming the n-paraffin-lean fraction to product areformate, the steps comprising:

a. subjecting said n-paraffin-lean fraction to reforming conditions inthe presence of hydrogen and a reforming catalyst, whereby reformingreactions occur and a reformate is obtained containing C C n-paraffins;

. introducing said reformate in vapor phase to one end of an adsorptionzone containing a bed of molecular sieve adsorbent to selectively adsorbnparaffins and recovering from the other end of said zone ann-paraffin-lean reformate, the amount of reformate so introduced beinginsufficient to saturate the molecular sieve adsorbent with C -Cnparaffins;

c. purging interstitial vapor from the adsorbent without substantialremoval of C r,--C n-paraffins therefrom;

. introducing feed naphtha in vapor phase to said one end of theadsorption zone to selectively adsorb n-paraffins therefrom, the amountso introduced being insufficient to displace C,,C nparaffins from theadsorbent bed;

e. recovering from said other end of the adsorption zone an effluentconstituting said n-paraffin-lean fraction and utilizing same asspecified in step (a);

f. purging interstitial vapor from the adsorbent without substantialremoval of C C, n-paraffins therefrom;

g. and desorbing the C,,C n-paraffins from the bed zone annparaffin-lcan reformate, the amount of reformate so introduced beinginsufficient to saturate the molecular sieve adsorbent with C .,Cnparaffins;

t reC Bl' Said n-p affinic fraCKiOn and c. purging interstitial vaporfrom the adsorbent rfig nfi the adsorbent for in p without substantialremoval of C C n-paraffins 6. A process according to claim 5 whereineach of h f R and is Carried out y lmroducing P g d. introducing feednaphtha in vapor phase to said 5 l l d the 5 ofther f d the d to Purgemterst" one end of the adsorption zone to selectively ad- Y one en 10sorb n-parafflns therefrom, the amount so in- 7. In a process forupgrading a feed naphtha comtroduced being Sufficient to displace CYC6posed of n-paraffin and non-n-paraffin hydrocarbons of paraffins fromthe adsorbent bed but insufficient the C -C range by separating the feednaphtha into nto displace crclz therefrom. paraffin-rich andn-paraffin-lean fractions and catalytirecovering from Said other of theadsorption zigotiz r e s lz s'sgiz i zf fracton to produce 15 zone aneffluent constituting said n-paraffin-lean 1 1 a subjecting saig n paraffin l ean fraction substan fracflon contammg C5-C6 mpamffms and uuhzmgtially free of C C n-paraffins but containing p i ep(a) h I C Cn-paraffins and derived as hereinafter Purging mterstiua vapor from t eadsorbent specified, to reforming conditions in the presence withoutslibstamlal remqval of n-paraffins of hydrogen and a reforming catalystwhereby therefrom and desorbmgthe n-Paraffins reforming reactions occurwith C -50 C n-paraf- F the bed to recover said n-paraffm-nch finspartially isomerizing to C -C isoparaffins and a regenerate theadsorbent for re-use m a reformate is obtained containing C C n-paraf-Step fins. 8. A process according to claim 7 wherein each of b.introducing said reformate in vapor phase to one Step? (c) and earnedout by lmmducmg Purge end of an adsorption Zone containing a bed of gasinto the said other end of the bed to purge interstimolecular sieveadsorbent to selectively adsorb nhydrocarbons from Sam one paraffins andrecovering from the other end of said

2. A process according to claim 1 wherein in each of steps C and F thepurge gas is introduced into the said other end of the bed to purgeinterstitial hydrocarbons from said one end.
 3. A process according toclaim 2 wherein in step E the introduction of said second feed isstopped before any substantial amount of any straight chain hydrocarbonappears in said effluent.
 4. A process according to claim 1 wherein instep E the introduction of said second feed is stopped before anysubstantial amount of any straight chain hydrocarbon appears in saideffluent.
 5. In a process for upgrading a feed naphtha composed ofn-paraffin and non-n-paraffin hydrocarbons of the C5-C12 range byseparating the feed naphtha into n-paraffin-rich and n-paraffin-leanfractions and catalytically reforming the n-paraffin-lean fraction toproduct a reformate, the steps comprising: a. subjecting saidn-paraffin-lean fraction to reforming conditions in the presence ofhydrogen and a reforming catalyst, whereby reforming reactions occur anda reformate is obtained containing C5-C12 n-paraffins; b. introducingsaid reformate in vapor phase to one end of an adsorption zonecontaining a bed of molecular sieve adsorbent to selectively adsorbn-paraffins and recovering from the other end of said zone ann-paraffin-lean reformate, the amount of reformate so introduced beinginsufficient to saturate the molecular sieve adsorbent with C5-C12n-paraffins; c. purging interstitial vapor from the adsorbent withoutsubstantial removal of C5-C12 n-paraffins therefrom; d. introducing feednaphtha in vapor phase to said one end of the adsorption zone toselectively adsorb n-paraffins therefrom, the amount so introduced beinginsufficient to displace C5-C12 n-paraffins from the adsorbent bed; e.recovering from said other end of the adsorption zone an effluentconstituting said n-paraffin-lean fraction and utilizing same asspecified in step (a); f. purging interstitial vapor from the adsorbentwithout substantial removal of C5-C12 n-paraffins therefrom; g. anddesorbing the C5-C12 n-paraffins from the bed to recover saidn-paraffin-rich fraction and regenerate the adsorbent for re-use in step(b).
 6. A process according to claim 5 wherein each of steps (c) and (f)is carried out by introducing a purge gas into the said other end of thebed to purge interstitial hydrocarbons from said one end.
 7. In aprocess for upgrading a feed naphtha composed of n-paraffin andnon-n-paraffin hydrocarbons of the C5-C12 range by separating the feednaphtha into n-paraffin-rich and n-paraffin-lean fractions andcatalytically reforming the n-paraffin-lean fraction to produce areformate, the steps comprising: a. subjecting said n-paraffin-leanfraction, substantially free of C7-C12 n-paraffins but containing C5-C6n-paraffins and derived as hereinafter specified, to reformingconditions in the presence of hydrogen and a reforming catalyst, wherebyreforming reactions occur with C5-50 C6 n-paraffins partiallyisomerizing to C5-C6 isoparaffins and a reformate is obtained containingC5-C12 n-paraffins; b. introducing said reformate in vapor phase to oneend of an adsorption zone containing a bed of molecular sieve adsorbentto selectively adsorb n-paraffins and recovering from the other end ofsaid zone an n-paraffin-lean reformate, the amount of reformate sointroduced being insufficient to saturate the molecular sieve adsorbentwith C5-C12 n-paraffins; c. purging interstitial vapor from theadsorbent without substantial removal of C5-C12 n-paraffins therefrom;d. introducing feed naphtha in vapor phase to said one end of theadsorption zone to selectively adsorb n-paraffins therefrom, the amountso introduced being sufficient to displace C5-C6 n-paraffins from theadsorbent bed but insufficient to displace C7-C12 therefrom; e.recovering from said other end of the adsorption zone an effluentconstituting said n-paraffin-lean fraction containing C5-C6 n-paraffinsand utilizing same as specified in step (a); f. purging interstitialvapor from the adsorbent without substantial removal of C7-C12n-paraffins therefrom; g. and desorbing the C7-C12 n-paraffins from thebed to recover said n-paraffin-rich fraction and regenerate theadsorbent for re-use in step (b).
 8. A process according to claim 7wherein each of steps (c) and (f) is carried out by introducing a purgegas into the said other end of the bed to purge interstitialhydrocarbons from said one end.